1. Field of Invention
This invention is directed to the "facing" or sharpening of rotary saw blades of the type having a plurality of teeth cut into the outer perimeter of a disc. This type of saw blade operates by rotating about a disc axis while the disc axis is moving relative to the material being cut. This relative movement may be effected with either the axis stationary or the material being cut stationary.
In many cases, the teeth are provided with a hard coating of a carbide material, resulting in a carbide tip used as the cutting portion of each saw tooth. The saw teeth may be uniform throughout the circumference or they may be of different sizes and spaced irregularly about the circumference. The cut-out spaces between the successive teeth are called "gullets."
In a type of saw blade called a "strobe saw blade," deep "rakers" extend from some of the gullets radially toward the center of the saw blade disc. Typically, two such rakers are provided and a carbide edge extends slightly from the planar surface of the disc at the raker. These rakers enable the saw blade to cut through materials which are likely to expand against the saw blade disc as the saw blade disc is progressing in its cutting operation. The rakers are used to shave this expanded material, thereby preventing the expansion from "jamming" the saw blade by rubbing against it. Such strobe saw blades are used, e.g. in the lumber industry for trimming uncured wood.
The deep rakers of strobe saw blades, by their very nature, cause difficulties in an automatic saw facing apparatus. This is because the automatic saw facing apparatus must grip the saw blade during the facing operation in order to prevent the saw blade from rotating during grinding steps and in order to hold the saw blade on the apparatus. Because the most advantageous location for gripping the saw blade is between the center axis and the teeth around the perimeter of the saw blade, these rakers, and particularly the carbide edges of the rakers will usually get in the way of the gripping means. While the carbide edges of the rakers can be hollow ground in order to make them essentially self-sharpening, it is necessary to face the successive teeth about the perimeter of the saw blade, despite the presence of the carbide edges of the rakers.
The type of applications in which strobe saws are employed, as well as the presence of the "rakers" results in a significant percentage of strobe saws having irregularly spaced teeth about their perimeters.
Since such strobe saws tend to have irregularly spaced teeth, automatic facing of the saw blades must be accomplished in such a way as to compensate for the varying spacing of the teeth.
2. Description of the Prior Art
Automatic machines to perform cutting operations on saw teeth are well known in the prior art. For example, U.S. Pat. No. 907,862 shows a machine in which a finger reciprocally driven by a wheel causes successive teeth to be moved forward. At the same time, an emery wheel is moved into engagement with the teeth in order to slant an outer perimeter of the teeth. However, the fixed relationship of the eccentric mounting of the finger and the emery wheel require that the apparatus be carefully indexed according to a given spacing of saw teeth on the saw blade. Such indexing requires skilled operation and would make the automatic facing of blades having irregularly spaced teeth difficult, if not impossible.
U.S. Pat. No. 4,111,075, shows a grinding machine in which an indexing finger turns a saw blade to a fixed location. The saw blade is then clamped between a pair of pads which are forced together by a clamping cylinder. It is necessary that those clamping pads be lightly biased during the indexing operation in order that only the desired rotation, i.e., that rotation caused by the indexing, take place. Such an arrangement does not provide for the indexing of saws having irregularly spaced teeth. More importantly, by the use of opposed clamping pads, a strobe would interfere with the operation of such a device and therefore a strobe saw could not be automatically faced. If a strobe raker is in engagement with the clamping pads, the saw blade would be permitted to pivot on the raker, thus causing excessive vibration.
U.S. Pat. No. 4,018,107 shows the use of a feed pawl operating on each successive tooth face. However, reciprocal operation of the feed pawl is effected by rotating cams, therefore making adjustment difficult. No means for clamping the saw blade between the center spindle and the teeth, while permitting the passage of a strobe saw raker, is disclosed, as a rotational position of the saw is maintained by the engagement of the grinding disc with the gullets between a tooth back and a precutting tooth.
The use of magnets to hold a cutting blade is shown in U.S. Pat. No. 3,766,806. However, these magnets are used to hold the blade down on the table. By using permanent magnets and by the use of an indexing detent which engages a blade remotely from the index position, the magnets are not used to cooperate with the indexing means to permit automatic facing of strobe saws. Furthermore, the automatic facing of irregularly spaced teeth is prevented by the indexing detent being remote from the index position.
Accordingly, it is an object of the present invention to provide means for automatically facing blades including carbide tipped strobe saw blades and saw blades having irregularly spaced teeth.
A further object of this invention is to provide means for facing saw teeth on a saw blade while gripping a portion of the blade between the saw teeth and the center spindle even where that portion may have surface interruptions or irregularities.
A further object of the invention is to provide readily adjustable means for indexing a wide variety of saw blades where the indexing means engages that saw blade tooth to be indexed, thereby placing that tooth in a position to be faced, irrespective of the regularity of tooth spacing. It is a further object of the invention to provide such saw tooth facing apparatus wherein the indexing means cooperates with a pair of electromagnetic gripping means in order to permit vibration to be reduced and to permit the facing of saw blades having irregular tooth spacing and/or irregularities on the surface between the saw teeth and the center spindle hole of the saw tooth.
It is a further object of this invention to provide automatic saw facing apparatus which is simple in construction and does not require complicated adjustments.
It is a further object of the invention to provide saw facing apparatus which uses hydraulic actuation and pressure switches to operate an automatic sequencing means. It is a further object of the invention to provide such simplified cutting apparatus which has a counting means to automatically face a predetermined number of saw teeth or to reface the saw teeth a predetermined number of times.
It is yet a further object of the invention to provide automatic saw facing apparatus which has an indexing means which reciprocates into a position which permits it to engage a successive tooth or to skip teeth during its automatic operation.
It is a further object to provide such apparatus which, by adjusting the stroke of retraction of an indexing means, the indexing means is able to index successive irregularly spaced teeth. It is yet a further object of the invention to provide automatic saw facing machine which is economical in operation. It is still a further object of the invention to provide automatic saw facing machine which has enhanced operation by indexing saw teeth with an indexing means which moves to an index position, permitting a saw tooth cutting wheel to engage the saw tooth at the index position and which provides a lubrication means to prolong the life of the saw tooth cutting wheel.
It is yet another object of the invention to provide a sequence programmer for causing a facing apparatus to execute the required sequence of steps for facing carbide tipped strobe saw blades.
Yet another object of the invention is the provision of a sequence programmer utilizing relays, responsive to position and pressure conditions, for controlling an indexing and a grinder advancing and retracting hydraulic operation.